1. Field of the Invention
The present invention relates to an endoscope apparatus and, in particular, to a structure of an endoscope that performs automatic focus control simultaneously with acquisition of an optically enlarged image of an object to be observed.
2. Description of the Related Art
A electronic endoscope apparatus includes an electronic endoscope (scope) having a CCD (Charge Coupled Device) and the like, which is a solid-state image pickup device, at a distal end thereof, a processor device, and a light source device, and displays an image of an object to be observed on a monitor by picking up an image of an object to be observed by the solid-state image pickup device on the basis of light illumination from the light source device and performing image processing with respect to picture signals by the processor device.
FIG. 6 shows a structure of a distal end of an endoscope with an objective lens moving mechanism in the related art which is applied to electronic endoscopes of this type. In FIG. 6, an observation window 3 is provided at a distal end surface of a supporting section 2 of a distal end 1 of the endoscope, and a CCD 6, which is a solid-state image pickup device, is arranged on the back side of the observation window 3 on an optical path with the intermediary of a prism 4 and a cover glass 5. The picture signals obtained by the CCD 6 are transmitted to the processor device via a signal line 7.
Arranged between the observation window 3 and the prism 4 is a first movable lens 9 and a second movable lens 10 which constitute an objective optical system, and hence a varifocal optical system is established. A holding frame 11 of the first movable lens 9 and a holding frame 12 of the second movable lens 10 are mounted to a cylindrical cam shaft 13 by fitting engaging holes 11A, 12A thereof on an outer periphery of the cam shaft 13. The engaging hole 11A is formed with a cam pin 15, and the engaging hole 12A is formed with a cam pin 16 so as to project therefrom, and the cam shaft 13 is formed with cam grooves 17, 18 at different inclination angles with respect to the axial line thereof. The cam pin 15 is engaged with the cam groove 17 and the cam pin 16 is engaged with the cam groove 18.
A linear transmission member 19 formed of a multicoil spring is connected to the cam shaft, and the other end of the linear transmission member 19 is mounted to a motor or the like provided in an operating unit. Therefore, by rotating the cam shaft 13 via the linear transmission member 19 by driving the motor or the like, the first movable lens 9 and the second movable lens 10 move in the fore-and-aft direction in the direction of the optical axis by engagement between the cam grooves 17, 18 and the cam pins 15, 16, whereby optical change in magnification power (enlargement) or the like is achieved.
On the other hand, as regards the endoscope, there exist a type in which focusing is achieved by driving a focusing lens by a rapid deformation piezoelectric actuator by operating an operating switch of an operating unit as disclosed in JP-A-6-22903.
Alternatively, as shown in JP-A-2002-263058, an endoscope having an automatic focusing mechanism is also manufactured. This automatic focusing mechanism is adapted to drive a movable lens for automatic focusing on the basis of focus estimating signals (high-frequency signals) extracted from the picture signals (predetermined distance measurement area). With the control of the automatic focusing mechanism, the automatically focused object to be observed can be observed on a monitor.
In the case of the endoscope apparatus in which the magnification power is changed optically as described in conjunction with FIG. 6, the magnification power is changed optically (observational distance, observational depth, and focal distance or the like are variable) by moving the second movable lens 10 in association with the movement of the first movable lens 9. In association with the change of the focal point, positional adjustment such as to reduce the distance between the object to be observed and the distal end of the electronic endoscope (scope) and correction of the focus are necessary. However, in an enlarged position, focusability is limited due to the observational depth. Therefore, if further detailed focusing can be performed automatically, an enlarged and clear image of the object to be observed can easily be acquired. In other words, in the related art, when being out of focus, it is necessary to perform focus adjustment operation by minutely moving the distal end of the endoscope for changing the distance with respect to the object to be observed, and such an operation is quite complicated.
On the other hand, since the diameter of the distal end of the endoscope is aimed to be small, an efficient structure and arrangement must be employed in order to provide an automatic focusing mechanism for performing focusing operation automatically in addition to the optical magnification power change mechanism.